Sunday, 7 February 2016

Stop signs

Drive for a few minutes in North America on a road that is not an arterial road and you will almost certainly see a stop sign somewhere. You will have to drive for a long time and take unusual routes to find the same in the Europe, and especially the Netherlands. One of the few times when a generalization about Europe is actually correct.

But why are Dutch roads so safe with these minor side streets and why do we often believe that stop signs are essential to safety? And why do we have so many, even as traffic managers admit that unwarranted stop signs are near universally disrespected?

Perhaps it comes down to our warrants. I don't have the Canadian manuals, but I do have the US ones. We follow the US in many areas of roadway design, if not for the slightly different signs and traffic lights, and our signs that say things in kilometres and metres, you could barely tell the difference.

"Section 2B .04 Right of Way Intersections"

The idea is that a through street should have the right of way over a minor street, makes sense, and also suggests it with certain volume conditions. It also suggests their use in at an unsignalized intersection where there is ordinarily traffic lights. I don't know where in a good street design you are likely to find them, in the Netherlands in modern designs, traffic lights are far less common. I count on a single street about 5 km long, Jasper Ave, more traffic lights than all of Assen. Most of the areas I can think of where there are a lot of traffic lights are in areas where traffic could be diverted and made into a low volume distributor, in an area suitable for pedestrianization or similar designs. Either way, this makes some sense because access roads are probably the only roads that should be uncontrolled.

Additionally, where minor roads intersect, where the volume for the intersection is more than 2000 vehicles per day, there is bad visibility or there is a bad crash record, 5 crashes in a 3 year period or 3 crashes in 2 years (that involve a failure to correctly assign the right of way) signs should also be used.

Fairly similar to the Dutch version.

But here is a key difference. It gives the option to use a yield sign OR a stop sign. It does not specify that a stop sign must mean the sightlines are very poor and that a road needs to have the right of way over the other road.

This is not what the Dutch use. They have that latter clause, which makes a huge difference.

It has another section dedicated towards stop signs.

It says firstly that a yield sign should be used where a stop sign is not needed at all times. This should be changed to a shall be used to force the engineers to install the yield signs.

The other statements include: 02 The use of STOP signs on the minor-street approaches should be considered if engineering judgment indicates that a stop is always required because of one or more of the following conditions:
  1. The vehicular traffic volumes on the through street or highway exceed 6,000 vehicles per day;
  2. A restricted view exists that requires road users to stop in order to adequately observe conflicting traffic on the through street or highway; and/or
  3. Crash records indicate that three or more crashes that are susceptible to correction by the installation of a STOP sign have been reported within a 12-month period, or that five or more such crashes have been reported within a 2-year period. Such crashes include right-angle collisions involving road users on the minor-street approach failing to yield the right-of-way to traffic on the through street or highway.
And: 
Support:
01 Multi-way stop control can be useful as a safety measure at intersections if certain traffic conditions exist. Safety concerns associated with multi-way stops include pedestrians, bicyclists, and all road users expecting other road users to stop. Multi-way stop control is used where the volume of traffic on the intersecting roads is approximately equal.
02 The restrictions on the use of STOP signs described in Section 2B.04 also apply to multi-way stop applications.
Guidance:
03 The decision to install multi-way stop control should be based on an engineering study.
04 The following criteria should be considered in the engineering study for a multi-way STOP sign installation:
  1. Where traffic control signals are justified, the multi-way stop is an interim measure that can be installed quickly to control traffic while arrangements are being made for the installation of the traffic control signal.
  2. Five or more reported crashes in a 12-month period that are susceptible to correction by a multi-way stop installation. Such crashes include right-turn and left-turn collisions as well as right-angle collisions.
  3. Minimum volumes:
    1. The vehicular volume entering the intersection from the major street approaches (total of both approaches) averages at least 300 vehicles per hour for any 8 hours of an average day; and
    2. The combined vehicular, pedestrian, and bicycle volume entering the intersection from the minor street approaches (total of both approaches) averages at least 200 units per hour for the same 8 hours, with an average delay to minor-street vehicular traffic of at least 30 seconds per vehicle during the highest hour; but
    3. If the 85th-percentile approach speed of the major-street traffic exceeds 40 mph, the minimum vehicular volume warrants are 70 percent of the values provided in Items 1 and 2.
  4. Where no single criterion is satisfied, but where Criteria B, C.1, and C.2 are all satisfied to 80 percent of the minimum values. Criterion C.3 is excluded from this condition.
Option:
05 Other criteria that may be considered in an engineering study include:
  1. The need to control left-turn conflicts;
  2. The need to control vehicle/pedestrian conflicts near locations that generate high pedestrian volumes;
  3. Locations where a road user, after stopping, cannot see conflicting traffic and is not able to negotiate the intersection unless conflicting cross traffic is also required to stop; and
  4. An intersection of two residential neighborhood collector (through) streets of similar design and operating characteristics where multi-way stop control would improve traffic operational characteristics of the intersection.

Stop signs are not needed when the volume is nigher, or where there is high speed on the main roadway. Crash records that indicate that a stop sign is likely to prevent a considerable number of collisions can support a stop sign, but visibility is what needs to be the factor. 

And in any case, why would a stop sign improve things over a yield sign? Both require the traffic seeing the sign to let other traffic go first, one requires a full stop at all times even without conflicting traffic, the other one does not. All way stop signs are an oddball, probably unique to North America, maybe Australia uses the same. Many of them would be good as mini roundabouts or regular roundabouts. Others might benefit as uncontrolled intersections, intersections without signs, signals or markings that govern the right of way, and others would benefit being 2 way yields. 

The Dutch have discovered that humans are not going to do that much based on what a single sign tells them unless there is a natural reason for wanting to do it. If you see a wrong way to a freeway sign, you know to turn back immediately, because you know very well that two directions of something like 80 km/h+ traffic head on it never good. If you see a stop sign, what gives you inventive to obey it? A yield sign at least is more self enforcing at locations where there is a main road because you know that they know that you are expected to stop and you are likely to crash into another car if you fail to yield. But even that isn't good enough. A raised table, often a continuous sidewalk where you cross an access road in an urban areas, visual priority and tight corner radii make places where you need to yield much more self enforcing, and they work for any remaining stop sign controlled intersections. 

Stop signs will not work unless there is something to make them look like they need to be obeyed beyond a police officer giving you a ticket at periodic intervals to a small minority of offenders. Speed limits in the US and elsewhere are going up on highways and freeways because they know that natural behavior is in places where it isn't doing harm should be legal. Why don't we apply similar logic to ordinary streets where the same human behavior is often the sensible behavior? 

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